Electrical apparatus



Feb. 8, 1927.

C. G. SMITH ELECTRICAL APPARATUS Filed Dec. 3l, 1921 45 the electrodes.

Patented Feb. s, 19,27.

UNITED STATES PATENT OFFICE.

CHARLES G. SMITH, OF MIEDVFORD,- MASSACHUSETTS, ASSIGNOR, BY MESNE ASSIGN- MENTS, TO RAYTHEON MANUFACTURING COMPANY,l `Oils" CAMBRIDGE, MASSACHU- SETTS, A CORPORATION OF MASSACHUSETTS. 'l

ELECTRICAL APPARATUS.

Application led December 31, 1921. Serial No. 526,095.

The present invention relates to electrical apparatus and more particularly toappara` tus of the type involving short path 'phenomena such as the apparatus disclosed in the application of Smith, Serial No. 415,536, filed October 8, 1920, and Patent No. 1,545,207, granted July 7, 1925. i

It has been shown that the use of two electrodes immersed in a suitable gaseous l0 medium and having their active surfaces spaced apart a distance which is insutlicient to normally permit ionization of the gas enables certain new and` valuable results to be obtained by controlling the paths of electrons between the active surfaces of the electrodes in sucha manner as to vary the ionization of the gas. In the aforesaid patent, this control ofv the paths of electrons is' ac- -complished through the use of a magnetic field applied in such a manner that Vthe paths of electrons leaving one electrode when this electrode acts as a cathode are sufficiently long to cause substantial ionization and consequent gaseous conduction, whereas the paths of electrons leaving the opposite electrode whenl the latter acts as a cathode are so short as not to cause substantial ioniza-` tion and gaseous conduction, making this form of apparatus in effect a rectifier` of 80 alternating currents. By a suitable control of these paths it will be obvious that such an apparatus may be caused to function as l0 carrying outpth'e invention, I employ two electrodes immersed in a gas and so located with respect to one another that all pathsare short e.\:cep't paths entering a hollow space through an opening in the surface of one of NVith a construction of this sort, a large number of positive ionsfcollect close to the inner cathode. surface'while current is being 'passed between the electrodes and a positive'space charge is created.- This space charge causes gaseous conduction,v to take' place between the electrodeswhen `the hollow electrode is negative but, l011l the other han-:l` no appreciable current passes inl Y the oppositedirection.l

In the actual construction of apparatus embodying this principle, it is sufficient that the electrodes be so constructed and arranged with respect to one another that all paths through the gaseous medium shall be suliciently short to prevent conduction except paths through an opening of proper size in one of the electrodes, and all paths available for conduction through the insulating medispace entirely surrounded by electrode ma-v terial 1s an advantage which can only be obtained with a tube embodying the new principles above set forth.

The accompanying drawing illustrates a form of tube embodying the new features of the present invention.

The illustrated embodiment of the inven tion shown in the drawing comprises a hermetically sealed receptacle 10 filled with helium or other suitable gas and having co-operating electrodes indicated generally at 12 and 28 immersed therein. The elec- .trode 12 comprises a hollow. cup 18 received within the upper end of a tubular member 16 andclosed by a 'disk 20. As indicated, the hollow cup 18 is provided with an upstanding neckor sleeve portion 22. LThe cooperating electrode 28 is carried by a tube 24 received within the tube 16 and mounted concentrically therewith, the tube I which the electrodes are immersed, this spac- I communication is afforded by the openingV 32 causes the device to conduct current when` the outer electrode 12 is negative. This characteristic of the device is due to the formation of a positive space charge in the area 30 ,after the operation of the tube has started. This positive space charge consists of a large number of relatively immobile positive ions which may persist in appreciable numbers from one cycle to the next andl which form a cloudv in the space opposite the opening. The effect of this chargeis to cause conduction to take place freely through the space between the pin 28 `and the interior of the hollow electrode when the hollow electrode is negative. On the other hand, when the electrode 12, which may be termed the solid electrode, is negative, no substantial current passes through the tube as all of the space available for conduction is either too short to permit cumulative ionization of the gas or else is blocked by the effect of the positive cloud. Furthermore, it will be observed that the gaseous discharge is oniined toa region which is completely surrounded by electrode material, avoiding the possibility of any stray ions or electrons bombardino' the Walls of the receptacle or other dielectric and setting up in consequence a charge, which `would tend to render the operation of the tube erratic. The inner electrode tube 24 vmay be conveniently supported upon the upper end of a projection 36 extending from the lower end of the receptacle 10 and formed of insulating material. This tube surrounds the glass projection closely without actually contacting withit in order that the heated material of the metal tube when in action shall not tend to crack the glass. In order to support the tube, it has been found convenient to insert a thin spacer ring 40 between the tube and the glass projection, as indicated. The tube may also be supported by a branching wire, which extends upwardly from the projection 36 and is connected to he innerwall of the tube, as indicated, this projection serving as one of the leading-in `wires. The outer electrode tube-16 projects downwardly below the end of the inner tube and is conected to a lip 42 projecting outwardly from a sleeve 44, this sleeve embracing the projection 36 closely and being supported by a shoulder 46 Larmes cast upon the projection as indicated. -With space separatino` the surfaces of the elec-I trodes are invarc-iably short with the exception of those in the ischarge s ace and that all of the spaces available or discharge through the msulating dielectric are suiciently long to avoid breakdown. l"urtherl more, the relatively hot walls of the electrode tubes 16 and 24 do not directly contact with the glass so that liability of the glass cracking isA avoided. Aside from these advann tages as enumerated, this type of device has the further advantage that an enclosing re ceptacle may be employed of any 'desired size with a comparatively large body oi gas imn mersed therein. This is a distinct advantage* as the convection currents set up this gas tend to dissipate heat from the elec trode tubes and permit a comparatively large current to be passed through the apparatus without detrimental eect. It will gbe observed thatthe outer electrode 12 constitutes the cathode when the apparatus is conducting. As the cathode naturally becomes hotter during the operation than the cooperating electrode, the dissipation of heat therefrom is facilitated owing to the fact that it is in direct communication with the comparatively large enclosing body of gas. v

The tube may be conveniently embodied in any suitable form of circuit such as shown in the drawing. This circuit may comprise a source of alternating current, indicated at 50, embodied in a primary circuit 52 and coupled with the tube circuit through the connection indicated at 54, the tube circuit having any suitable form of load, indicated at 56, connected therein, together with capacity and inductance, as may be needed with circuits of this character.

It will be understood by those skilled in the art from the foregoing description that this type of tube functions according 1o the broadly new principle underlying the operation o the apparatus disclosed in the Smith application and patent above referred to. This principle recognizes iirst that it is possible to so separate electrodes immersed in a gas that cumulative ionization and conduction may be prevented. This principle is here utilized to limit the discharge to a small area where it can be so controlled by the effect of a space charge as to be uni-directional.

In the Smith application abovel referred to, a tube which normally.insulates against conduction in eitherdirection may be caused to conduct in one direction bythe imposition of a magnetic ield'ot the requisite strength, which diverts'and lengthens'thc paths of electrons sufiiciently to set up cumulative ionization. According to the present disclosure, this same result is eiiected titi by the proper design and construction of the opposing electrodes in such a -manner that a space charge effect is created at the discharge point to allow conduction when the hollow electrode is negative, the tube insulating against conduction in the usual manner when the opposing electrode isnegative.

This is due in considerable measure to the widely dissimilar areas of the active surfaces of the cathode and anode (the interior surface of the large cathode and the upper end of the small anode) in con'unction with the electrical characteristics o the gas filling. Then using helium the anode loss is abnormally low during the half cycles when the cathode is negative due to the fact that helium is a monatomic gas comparatively free from negative ions which magnify the anode losses. Thus there is less heating at the anode and less tendency for the anode to disintegrate. Consequently, the anode may be made smaller than in other rectifiers of the large and small electrode type filled with air, thereby affording more complete rectification by virtue'of the greater difference in area of the active surfaces of the electrodes.

When using helium the reverse current, during the half cycles when the anode is negative, is abnormally low and consequently this rectifier affords more complete rectifica-tion for this reason also, and owing to this low reverse current, the anode losses and disintegration are also lower during reverse half cycles. This desirable phenomenon is believed to be due to the abnormally long mean free path of electrons in monatomic gases, particularly helium.

By restricting the path of approach to the small anode by wall 22, the rectifying characteristics are further improved; and by virtue of the close spacing betweenv wall 22 and the anode, effective insulation results from the aforesaid short path principle. As described and claimed in companion application Serial No. 464,358, filed April 2l, 1921, the monatomic gas also has thel function of permitting the short spacing between the electrodes to be made longer for the same degree of insulation, thereby facilitating the manufacture.

lVhile argon and other inert gases have longer mean free paths for slow speed electrons (below ionizing velocity), I have discovered that for high speed electrons (above ionizing velocity) helium is unique in that it has a much longer mean free path. Consequently, in a gaseous conduction tube helium minimizes disintegration of the electrodes (when negative) for the following reasons: The average distance from the electrode at which ions are produced by high-speed electrons in helium is greater, and the ions in falling through this greater .distance to the electrode are more retarded by interveningr molecules so that they impinge upon the electrode with less force, it being known that the velocity of the ions when unobstructed by intervening molecules depends upon the voltage drop and not upon the distance they have to travel to the electrode. l

In order to avoid variations in the gas pressure and disintegration of the hollow cathode member, it has been found desirable to provide a small quantity of metallic tin inside of the space 30. This metallic tin may conveniently be amalgamated to the iron or other metal comprising the cup 18, forming a thin coating over the internal surface. During the normal operation of the tube this tin is in a liquid condition. When the tube ceases to operate and the electrodes are reduced in temperature, the tin hardens into a solid form so that the tube may be freely handled without liability of the tin leaving the hollow space 30. Even in the molten condition it is extremely difficult for the tin to run out or be shaken out of the hollow cathode due to the configuration of this member with the upstanding sleeve 22 and to the attraction of the tin for the underlying and supporting metal.

Thus it will be evident that the invention exemplified by the embodiment above described has the following unique characters istics. The anode surface is presented to the cathode surface through a restricted opening to which the anode is closely adjacent, the obstruction which contains the opening preferably being of metal and forming a part of the hollow cathode. In a glow-discharge (non-arcing) tube having a solid (non-vaporizable) cathode surface, this arrangement has the unique function of trapping ions in the restricted region adjacent the cathode surface, thereby tending to restrict back current during alternate halfcycles when the anode is negati ve. By making the space between the anode and the periphery of said opening sufficiently short. (as described above and in said co-pending application) the space is insulating at normal potentials. A gap of similar length may be provided between the anode and the exterior of the cathode and/or a tube (16) surrounding the anode. The cathode has a. flan e surrounding said opening, preferably insi( e the cathode, and the anode preferably projects into the neck'forined by the flange. However, the anodepreferably terminates short of the mouth of the neck to provide greater space charge adjacent the active face of the anode more effectively to restrict back current from anode to cathode. The mouth 125 of the cathode neck constitutes an orifice providing an ionizing path or passage and the cathode is large enough in diameter to provide an opposing face to the entire outer edge of the anode. The opposing surfaces of arts 18 and 26 constitute broad plane sur aces arranged close together with a gap therebetween Whose ylength is less than or at least comparable to the mean free pathv of electrons 1n the space. The part 2O constitutes shielding means in line with the aforesaid ionizing passage; and the neck 22 comprises a cylindrical wall extending at substantially right-angles to the face of the anode.

From the foregoing it will be evident that the anode projection 28 and the surrounding cathode flange 22I constitute means additional to the space charge for selectively causing electrons passing in different directions through the gas to take paths of Widely different lengths. A modification of such means is described and claimed in my copending application Serial N o. 654,642.

Each end of the cylindrical cathode is closed, the upper end by a separately formed cover 20 and the lower end by the integrally formed cover 18, the space within the cylindrical cathode thus being entirely confined except for the restricted opening 32 in cover i8.

A novel feature of the invention consists in that means are provided for preventing the discharge, as well as radiationfrom the discharge, from reaching any insulation material, thereby prolonging the useful life of the tube. ln the illustrative embodiment the parts lll, 16 and 26 entirely shield the insulating stem 36 as well as the interior surface of the tube l0. rlhis is preferably aecomplished by confining the active area of the cathode to the interior thereof and confining the active area of the anode to that portion presented to the interior of the cathode. For this purpose I preferably employ a member (such as 26 in the illustration) which extends outwardly from approximately the diameter of the anode at least to approximately the diameter of the opening. rllhis member preferably has a surface spaced from one electrode a distance substantially confined to the mean free path of electrons in the gas, this short gap being disposed between member 26 and the cathode in the illustration.

AThe invention is also characterized inthat the current (whether gaseousor metallic conduction) is entirely confined to the aforesaid restricted opening. lhus in the illustration all of the current flows through the restricted opening 32, by metallic conduction through that portion of the anode disposed in the opening and by gaseous conduction' from the upper end of the anode to the lupper end of the opening defined by neck 22.

In a generic sense the term hollow cathode includes a cathode whose active surface only partially surrounds a gaseous medium so that the medium immediately adjacent the active surface is more or less pocketed 4or confined.

Another feature of the invention consists l in that the active area of the anode is small in comparison with the total surface of the anode""(in the illustrative embodiment only the tip of the anode 28 is active), whereby the heat generated at the active area of the anode by the back current during halfcycles when the anode is negative may be dissipated much more rapidly. Owing to this unusually rapid dissipation of heat the current density may be increasedv without heating the active anode surface hot enough to cause arcing. The larger permissible current density permits the use of a higher gas pressure, the density of the back current being approximately proportional to the square of the density of the gas. Thus the relatively small anode surface net only is important in itself to prevent arcing, but it permits the use of a higher pressure which protects the cathode as described in prior application Serial No. 464,358.

While it is preferred to employ the specific construction and arrangement of parts shown and described it will be understood that this construction and arrangement is not essential except so far as specified in the claims and may be changed or modified without departing from the broader features of the invention.

By having the free end of the anode (upper end in the iilustration) terminate in the region of the opening in the obstruction between the active surfaces of the cathode and anode, the tube is rendered much: quieter when used in connection ywith radio sets or other telephone transmission and at the same time the tube starts operation more easily. 4

The invention having been described, what is claimed is:

l. Electrical apparatus comprising a hollow electrode having an opening therein, another electrode presented to the interior of the hollow electrode through said opening and having its free end terminating in the region of the opening, and means for obstructing discharge between the second electrode and the exterior of the hollow electrode.

2. Electrical apparatus comprising a hollow electrode having an opening therein, another electrode presented to the interior of the hollow electrode through said opening, the active area of the second electrode being-*confined approximately to one end thereof and to the cross-Section area of said opening, and means for obstructing discharge between the second electrode and the exterior of the hollow electrode.

Electrical apparatus comprising a hollow electrode having an opening therein, another electrode presented to the interior of the hollow electrode through s aidopening and having its free end terminating m thc region of the opening, and means for obstructing discharge between the second electrode and the exterior of the hollow electrode, said means having a surface spaced from one of the electrodes a distance comparable to the mean free path of electrons in the space. v

4. Gaseous conduction apparatus comprising electrodes received in the receptacle hav-- of the hollow electrode through said opening, the active area of the second electrode being confined approximately to one end thereof and to the cross-sectional area of said opening, and means for obstructing dis,-

' charge between the second electrode and the exterior of the hollow electrode, said means having a surface spaced from one of the electrodes a distance comparable to the mean free path of electrons in the space.

6. An electrical apparatus comprising a gas filled receptacle, a plurality of electrodes immersed in the gas within the receptacle and having their opposing surfaces spaced in close proximity, means for producing a' gaseous discharge in the space separating the electrode surfaces, and means for confining the gaseous discharge to a region entirely. surrounded by electrode material.

7. A gaseous conduction rectifier comprising a sealed tube containing a hollow cathode encompassing a large free ionization space and having an opening at one side, an anode presented to the interior of the hollow cathode through said opening, and means for substantially confining the active area of the cathode to the interior thereof.

8. An electrical apparatus comprising a gas filled receptacle, a hollow electrode immersed in the gas and having atubular portion'extending inwardly into the space surrounded by the hollow electrode, a cooperating electrode having a projection extending part way into the opening formed by the tubular portion of the hollow electrode, and means for creating an electric field in the space separating the electrode.

9. A gaseous conduction rectifier comprising a tube containing a hollow cathode having a restricted opening at one side, an

.anode presented to the interior of thel hollow cathode through said opening, and means'n- .cluding said cathode for shielding ythe enti re tube from the discharge between cathode and anode.

l0. A gaseous discharge rectifier containing gas, a hollow cathode having an opening therein, another electrode presented to the interior of the hollow cathode through said opening, and means for confining the active surface of the hollow cathode to the interior thereof.

11. A gaseous conduction tube containing a hollow cathode having an opening therein, an anode presented to the interior `of the hollow cathode through said opening, insulation material for supporting the cathode and anode, and means for preventing the, discharge from reaching any msulatlon maf terial through said opening.

12. A-gaseous conduction tube com risl;

ing a hollow cathode havingl a restricted opening, an anode presented to the interior of the hollow cathode through said opening,

and means including a member in ljuxtaposition to the cathode for vsubstantially con? fining the current to said opening.

13. In a rectifier, a small electrode, a hollow cathode arranged with voneend adjacent the other electrode and having a central 1on1z1n space, the activearea of the/hollow cathode eing confined to said space.

14. A- tube in which the current bridges.

the gapbetween the electrodes by gaseous conduction comprising, ahollow cathode I formed of two parts, one part `arranged to provide an. ionizing -pocket and one part having a restricted opening, an anode presented to saidpocket through said opening, and means 4tov confine-the -current to said opening. W v- 15. An electric discharge tube' comprising la hollow cathode having a restricted discharge opening,.and.an anode presented to the interior of the cathode through said.

opening, andmeans for confining the active area of the cathode tothe vinterior thereof,

said means providing an insulating space ius between the anode and the exterior ofthe cathode so short that the electrons passing directly across said space produce insuicient ionization to render the space conducting at potentials which produce conduction v betweenthev anode and the interior of the cathode. 4 f

16. An electric discharge tube comprising a hollow electrode having a restricted discharge opening, and a second electrode presented to the interior of the hollow' electrode through Vsaid opening, and means for confining the active area of the cathode to the interlor thereof, said means providing an insulating space between the second electrode and a portion of the hollow electrode surrounding said opening so short that electrons passing directly across said space produce lnsufiicient ionization; to render the space conducting at potentials which produce conduction between the second electrode and the interior of a hollow electrode.

17. An electric discharge tube cmnprising a hollow cathode having a dischargeopening, an anode presented to the interior of the cathode through said opening, and a tube surrounding one of the electrodes adjacent the other electrode with a space between the tube and one of the ,electrodes so' short that electrons passing directly across"- the space produce insuiicient ionization to render the space conducting at potentials which produce conduction between the anode and the interior of the cathode.

18. An electric discharge tube comprising a hollow cathode having a discharge opening, an anodeihaving a surface presented to the interior of the cathode through said opening, and means for confining the active area of the anode to said surface, said means including a tube surrounding the anode adjacent lthe cathode with a space between the tube and anode so short that electrons passing directly across the space produce insufficient ionization torender the space conducting at potentials which produce conduction between the anode and the interior of the cathode.

i9. A gaseous discharge tube containing a hollow cathode formed of two parts engaging around their peripheries, one part being cupped to provide an ionizing pocket and one part having a restricted opening, an

P anode presented to said pocket through said opening, and means surrounding the anode at the opening and extending outwardly at least approximately to the diameterof the opening to vprevent discharge from the outside o the hollow cathode.

`20. A gaseous conduction device comprising a hollow cathode with an opening therein, the diameter of the opening being smaller than the interior diameter of the hollow cathode, and an anode projecting into the hollow cathode through said opening.

2l. A gaseous conduction device comprising a hollow cathode with an opening therein, the diameter of the opening beingsmaller than the interior diameter of the hollow cathode, and an anode projecting into the hollow cathode through said opening, the space between the "anode and the periphery of said opening being insulating at potentials which produce conduction between the anode and the interior of the cathode.

22. A glow-discharge tube comprising an electrode having an electron emitting surface which is 'solid at room temperatures, another electrode having an electron receiving surface, an obstruction between said surfaces having a restricted discharge opening,

and means inside the tube for confining substantially all the current to said opening.

Lemire Q3. A glow-discharge device comprising an` electrode having au electron emitting surface which is solid at room temperatures, another electrodo having an electron receiving surface, an obstruction between said surfaces having a restrictcddischarge opening, the anode surface. lying in close juxtaposition to said opening, and means for restricting discharge between said electrodes except through said opening.

24. A gaseous conduction device comprising an obstruction having an opening therein, a cathode surface on one side of the opening, an anode surface presented to the cathode surface through said opening, and means obstructingy discharge through the space between the lobstruction and anode around said opening.

25. A gaseous discharge tube comprising an obstruction having an opening therein, a cathode surface on one side of the opening, an anode surface 'presented to the cathode surface through said opening, and means including a member extending outwardly from approximately the diameter of said anode surfaceto restrict the gaseous discharge to said cathode surface.

26. in a rectifier, a vacuum tube, two electrodes within said tubehaving their adjacent faces arranged so close together as to minimize ionization between them under one direction of applied potential, one of said electrodes .having an orifice providing an .ionizing path and constituting a cathode,

and the other electrode constituting an anode, the diameter of the cathode being larger than that of the anode to provide an opposing face to the entire outer edge of" the anode. l

27. A aseous conduction rectifier comprising a ho low cathode encompassing a large free ionization space and havingan opening at one side, an anode projecting into the hollow cathode through said opening and means for substantially confining the active area of the cathode to the interior thereof.

28. A gaseous conduction rectifier having an arrangement of electrodes, including a hollow cathode and an anode, in which the cathode functions below the temperature at l which the operation is dependent upon thermionic emission from the cathode, the active area of the cathode being sutliciently larger than that of the anode to produce gaseous conduction with a potential drop in one direction which when applied in reverse direction will not produce gaseous conduction of the same order of magnitude, and monatomic gas around the active area of the anode to reduce reverse current and anode losses. v

29. In a half-wave rectifier, a vacuum tube, two electrodes mounted therein with their adjacent faces close together, one of said electrodes constituting a cathode having an lllll llO Cil

ionizing chamber open toward the other electrode and closed at its opposite end, and means for substantially confining the discharge to said chamber.

80. G aseous conduct-ion apparatus coinprising a gas-filled receptacle, an electrode immersed within the receptacle and a second electrode having an opening communicating with a. restricted space to permit the formation of a space charge, and means in addition to the space charge for selectively causing electrons passing in different directions through the gas to take paths of widely different lengths.

31. An electrical apparatus comprising a.

gas-filled receptacle, closely spaced electrodes immersed therein, one of the electrodes having an opening communicating with a hollow space to allow formation of the space charge, and a conducting surface at the opening to selectively cause electrons to take paths of different lengths depending upon the direction of passage through the gas.

32. An electrical apparatus comprising a gas-filled receptacle, an anode and a cathode immersed therein and having opposing surfaces spaced apart a distance which is comparable to the mean free path of electrons in the gas, the cathode being provided with an opening communicating with a hollow space to permit formation of a space charge,

Aand a conducting surface placed opposite the opening to limit the paths of electrons passing from the anode to the cathode to distances which are suiicienty short to prevent ionization.

33. An electrical apparatus comprising a gas-filled receptacle, an anode, a cathode having a surface provided with an opening and spaced from the surface of the anode a distance which is short and comparable to the mean free path of electrons in the gas, a sleeve surrounding the opening to provide a passage communicating with a gaseous region adapted to pci-mit the formation of a space charge of positive ions upon impressing an electric eld between the anode and the cathode, and a conducting surface placed near the end of the passage.

34. A gaseous conduction rectifier comprising an anode, and a cathode whose active area is suliciently larger than that of the anode to produce gaseous conduction with a potential drop in one direction which when vapplied in reverse direction will not produce gaseous conduction of the same order of magnitude, and'means for confining the discharge to said active areas including surfaces spaced apart appreciably but insuiiciently to permit substantial ionization by electrons travelingdirectly across the space therebetween.

35. A gaseous conduction rectifier having an arrangement of electrodes, including a hollow cathode and an anode, in which the cathode functions below the temperature at which the operation is `dependent uponithermionic emission from the cathode, the active area of the anode being small in relation to the total area of the body of conducting material in conductive relation to the said active area in the rectiier.y

36. A gaseous conduction rectifier comprising a non-incandescent cathode, an elongate anode having one end presented to the cathode, and means for conning the active area of the anode to the tip ofsaid end.

37. A gaseous conduction rectifier having an arrangement of electrodes in which the back current is limited chiefly by space charge at the anode, the anode comprising a body, the active area of which is small in relation to the total area of the body of conducting material in conductive relation to said active area.

CHARLES G. SMITH. 

